1. Field of the Invention
The present invention is an air or gas injection collar for use in oil and gas drilling operations. In particular, the present invention is directed towards an apparatus in the form of a cylindrical sleeve that is coupled into a drill casing pipe to provide for specialized introduction of air or gas into the drill casing, as well as methods for its installation and use.
2. Description of the Prior Art
Mankind has been drilling for oil and gas for well over a century. Current methods and apparatus for drilling in the ground for oil or gas make use of an open-ended drill bit that is attached to the end of a continuously extended drill pipe. The drill pipe is rotated causing the drill bit to dig down into the earth. Additional lengths of pipe are attached end-to-end as the drill bit continues to dig down, creating a lengthy shaft. The earth, rock, chips and debris that are dislodged by the drill bit are removed by pumping specialized material (often referred to as “mud”) down through the drill pipe. This material exits through the open end of the drill bit and returns to the surface around the outside of the drill pipe through the earthen shaft that has been dug by the drill bit, carrying the dislodged material with it. At the surface, the dislodged earth, rock, chips and debris are separated from the mud which is recycled and sent back down through the drill pipe to repeat the process.
In order for the mud to bring the dislodged material to the surface, it is necessary for the sides of the shaft that has been cut into the earth to be of sufficient strength. It is not uncommon for a drill shaft to extend down hundreds if not thousands of feet. The mud that is pumped down through the drill pipe forms an annular column around the pipe as it returns to the surface, forming a tall column of mud and dislodged material. This results in extreme pressures per square inch, particularly at the bottom of the shaft. It is often the case that the layers of rock, sediment or other geologic material through which the shaft has been dug are not sufficiently strong to withstand these pressures, resulting in the mud and debris traveling laterally into the weaker earthen layers, instead of returning to the surface. This is undesirable and wasteful of the very expensive and specialized “mud” that is used. Further, if enough of the specialized mud is lost, the lack of pressure and lubrication in the well can cause further fracturing of the weaker earthen formations and damage to the drill pipe. If portions of the earthen formation fall into the annulus of the drill pipe they can be come firmly lodged, potentially resulting in the loss of both the pipe and the well.
It is common in the drilling industry to insert drill casing along the sides of the shaft once a certain depth is reached. The drill casing is simply a hollow cylindrical wall made up of segments of pipe that are inserted into the earthen shaft. Once the casing is inserted and cemented into place, then drilling can resume, with the drill pipe extending down the center of the casing and beyond into lower geological layers.
The conventional method for dealing with the problem of weak geologic layers is to reduce the weight of the mud that is returning to the surface by adding air to it. This is accomplished by routing an air pipe down the outside of the drill casing, and attaching this pipe to the drill casing at as low (deep) a location as practicable as shown in U.S. Pat. No. 2,726,063. The air pipe connects to an opening on the drill casing which air that is pumped down from the surface is introduced to the inside of the casing. This air is added to the annular column of mud and debris that is rising inside the casing, causing it to have less density, and hence less weight. This reduces the weight of the overall column of mud and debris, reducing the pressure on the mud and debris below the end of the casing where the weaker geologic layers may be found. An alternative method for introducing air is found in U.S. Pat. Nos. 3,497,020 and 3,534,822 which disclose providing an annular column of air inside the drill pipe or casing that is mixed with the returning mud through a series of ports. Both of these inventions require at least one extra cylindrical casing wall and both waste valuable interior casing space to provide the column of air, greatly increasing the cost and diameter of the drilling assembly.
Unfortunately, the introduction of pressurized air can increase frictional erosion inside the casing. A single inlet, or multiple uncontrolled inlets for introducing pressurized air into the drill casing effectively turn the rising mud and debris into a sandblaster that wears against the rotating central drill pipe. The friction caused by the sand and debris that is thrust against the drill pipe by the pressurized air eventually weakens the drill pipe and shortens its useful life. This is undesirable since the drill pipe is otherwise reusable, and must be strong enough to transmit the rotational force from the surface down to the drill bit in order to grind into layers of rock.
Another method for inducting air into the specialized mud is illustrated in U.S. Pat. No. 5,873,420 which discloses an air conducting tube that is provided on the inside of the drill pipe for introducing air to be mixed with mud at the drill bit. This tube runs the entire length of the drill pipe terminating above the bit where a valve, solenoid opener and centering devices are all deployed. However, the location of these devices inside the drill pipe is not only likely to interfere with the smooth flow of mud inside the drill pipe, it also increases the chances of a malfunction (or non function) since the high pressure and movement of the mud may prevent the solenoid from operating properly. In addition, failure of any of these components requires removal of the entire drill pipe for replacement.
It is therefore desirable to provide an apparatus and method for reducing the weight of the returning drilling mud without causing unnecessary frictional wear on the drill pipe, or interfering with normal drilling operations.